1. Field of the Invention
The present invention relates generally to the field of power supplies and more specifically to multi-voltage power supplies suitable for use in a universal airplane ground support equipment cart.
2. Description of the Related Art
When an airplane is on the ground with its engines shut down, the airplane is typically unable to provide power for its electrical systems and chilled air for its air conditioning systems; and some airplanes are also unable to provide liquid coolant for some critical electronic (or “avionic”) components. It is customary to connect such a grounded airplane to an airplane ground support equipment system. Such a system may have its components mounted upon a mobile equipment cart that is called an airplane ground support equipment cart and that may be parked, placed, or mounted conveniently close to an airplane requiring ground support. Such a cart typically contains an air conditioner that can provide conditioned and cooled air to an airplane plus an electrical power converter that can transform power drawn from the local power grid into power of the proper voltage (AC or DC) and frequency required by the airplane. Such an airplane ground support equipment cart may also contain a diesel engine connected to an electrical generator that enables the cart to provide both air conditioning and also electrical power for an airplane without any connection to the local power grid. And if an airplane requires a source of cooled liquid for its electronics, some carts may also include a source of liquid coolant, typically a polyalphaolefin, or PAO, heat transport fluid or liquid coolant.
As discussed when an airplane is on the ground with its engines shut down, the airplane is typically unable to provide power for its electrical systems; it is customary to connect such a grounded airplane to an electrical power supply. Such a power supply may have its components permanently mounted in a fixed location inside a facility, outside a facility on a tarmac, flight line or similar area, or the power supply may be mounted on a mobile platform such as a trailer to allow the power supply to be transported between locations. The output cables of this converter may connect directly to the aircraft if the location permits, or connected to a distribution system in order to supply power to several locations. The electrical power converter transforms power drawn from the local power grid into power of the proper voltage (AC or DC) and frequency required by the airplane. It is possible that a facility or location may need one type of power at the time the converter is initially installed, and then require a second type of power as new aircraft arrive on location.
Some airplanes require their electrical power to be adjusted to 115 volts of alternating current (A.C.) which alternates, or flows back and forth, 400 times each second (115 volts, 400 Hz A.C.). Other airplanes require 270 volts direct current (270 volts, D.C.) that does not flow back and forth.
In the past, particularly with regard to military airplanes, such converters supplied either 400 Hz AC or 270 VDC power depending on the particular type of aircraft, but not both. A second converter would need to be acquired if the need arose for the other type of power.